[Dose and timing of normal saline resuscitation on endothelial glycocalyx in early septic shock].

OBJECTIVE: To observe the effect of different doses and timing of normal saline (NS) resuscitation combined with norepinephrine (NE) on endothelial glycocalyx in rabbits with early septic shock.

METHODS: Thirty New Zealand male rabbits were randomly divided into sham group, model group, 30 mL and 60 mL timely resuscitation groups (30 mL and 60 mL timely group), and 30 mL delayed resuscitation group (30 mL delayed group) with 6 rabbits in each group. The rabbit model of septic shock was reproduced by cecal ligation and puncture (CLP). The rabbits in sham group were only received abdominal cavity open without cecal and ligation. The rabbits in 30 mL and 60 mL timely groups and 30 mL delayed group were intravenous infused with 30 mL/kg or 60 mL/kg NS immediately or 1 hour after model reproduction for 1 hour, and the mean arterial pressure (MAP) was maintained over 75 mmHg (1 mmHg = 0.133 kPa) compared with intravenous pumping of 0.02-0.05 μg×kg-1 ×min-1 NE followed by 5 mL/h NS infusion till the end of the experiment. The rabbits in sham and model groups were only given 5 mL/h NS. The changes in arterial blood gas before and immediately after resuscitation were observed in three fluid resuscitation groups. The internal jugular vein blood was collected at 0, 3, 6 hours after model reproduction. The levels of syndecan-1 (polysaccharide envelope marker) in plasma were determined by enzyme linked immunosorbent assay (ELISA). The rabbits were sacrificed at 6 hours after model reproduction, and the lung tissue was harvested. Western Blot was used to determine the protein expressions of intercellular adhesion molecule-1 (ICAM-1), matrix metalloproteinase 2 (MMP-2) and syndecan-1. The positive expression of syndecan-1 in lung tissue was observed by immunohistochemical method.

RESULTS: (1) Blood gas analysis: compared with the results before resuscitation, the levels of lactic acid (Lac) after resuscitation in three fluid resuscitation groups were significantly decreased, especially in 30 mL timely group; the central venous blood oxygen saturation (ScvO2 ) was significantly increased, especially in 30 mL delayed group. Oxygenation index (PaO2 /FiO2 ) was improved in 30 mL timely and 30 mL delayed resuscitation groups, which was decreased in 60 mL delayed group. (2) Plasma marker: compared with sham group, plasma syndecan-1 level in model group was significantly increased with a time-dependent manner. Plasma syndecan-1 levels at 3 hours in 30 mL timely and 30 mL delayed groups were significantly decreased as compared with those of model group (ng/L: 138.0±2.4, 139.7±15.7 vs. 161.5±4.1, both P < 0.05), but it was significantly increased at 6 hours in 30 mL delayed group (ng/L: 213.1±19.4 vs. 206.4±15.5, P < 0.05). The plasma syndecan-1 levels at 3 hours and 6 hours in 60 mL timely group were significantly higher than those in model group (ng/L: 233.0±28.9 vs. 161.5±4.1, 252.3±27.2 vs. 206.4±15.5, both P < 0.05). (3) Protein expression in lung tissue: compared with sham group, the protein expressions of ICAM-1 and MMP-2 in lung tissue of model group were significantly increased, and syndecan-1 protein expression was significantly decreased. After 30 mL timely or 30 mL delayed resuscitation, the protein expressions of ICAM-1 and MMP-2 in lung tissue were significantly decreased, and syndecan-1 protein expression was significantly increased, especially in 30 mL timely group, which showed statistical differences as compared with those of model group (ICAM-1 protein: 0.56±0.09 vs. 1.04±0.05, MMP-2 protein: 0.83±0.15 vs. 1.06±0.06, syndecan-1 protein: 2.09±0.08 vs. 0.99±0.03, all P < 0.05). The change tendency of protein expressions in 60 mL timely group was opposite to the other two resuscitation groups. (4) Immunohistochemistry: the positive expression of syndecan-1 in lung tissues was significant in the sham group, and it was lowered in model group. The positive expression of syndecan-1 was increased after 30 mL timely or 30 mL delayed resuscitation, but further weakened in 60 mL timely group.

CONCLUSIONS: The dose and timing of resuscitation with NS in septic shock can affect pulmonary vascular endothelial glycocalyx function. The timely resuscitation with 30 mL NS in combination with NE plays a protective effect on endothelial cell and glycocalyx. However, NS resuscitation which was not timely or excessive infusion can make the glycocalyx degradation more obvious, resulting in increased endothelial permeability, microcirculation damaged, thus aggravate lung injury.